Apparatus and method for controllable gain and phase matching in an optical data storage system with source noise subtraction

An apparatus and method for reducing optical source noise and other common-mode system noise in a data signal read from an optical storage medium. An exemplary apparatus in accordance with one aspect of the present invention includes a first detector to generate the data signal by detecting a return beam resulting from application of a radiation beam to the medium; a second detector to generate a source monitor signal by detecting radiation from an optical source providing the radiation beam; a correction circuit adapted to receive the data signal and the source monitor signal and generate a corrected data signal therefrom; and means for controlling the gain of a signal path of at least one of the data signal and the source monitor signal in response to, for example, low-frequency amplitude differences between the data signal and the source monitor signal. One or more delay lines may be included to provide phase matching of the data signal and source monitor signal at the correction circuit input.